code: def __make_buf_var_refs(info, buf_var_lives):
      # buf_var_refs is to store buffer indices of buffers required in each Function
      actual_buf_num = __count_actual_buf(info, buf_var_lives)
      shape = (len(info._network.function), actual_buf_num)
      buf_var_refs = np.empty(shape, dtype=np.int32)
      buf_var_refs[:] = -1
  
      # fill buf_var_refs based on buf_var_lives
      for func_idx, _ in enumerate(info._network.function):
          crsr = 0
          for buf_idx, buf_var_life in enumerate(buf_var_lives):
              if buf_var_life.needed_at(func_idx):
                  buf_var_refs[func_idx][crsr] = buf_idx
                  crsr += 1
              else:
                  pass  # only focus on buffers used in this func
  
      return buf_var_refs
  
file_path: nnabla/python/src/nnabla/utils/converter/nnablart/save_variable_buffer.py
imports: import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: __make_buf_var_refs(info, buf_var_lives) and returns: buf_var_refs